<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
    function yve(){
      let a=+prompt('输入余额')
      let b=+prompt('食宿消费')
      let c=+prompt('生活消费')
      return a-b-c
    }
    alert(`剩余${yve()}`)

  </script>
</body>
</html>